Inexpensive nanoparticles in a gel can replace traditional materials used to create holograms at a much lower cost, researchers report.

Holograms can be created by using magnetic fields to alter the path of light, but the materials that can do that are expensive, brittle, and opaque. Some only work in temperatures as cold as the vacuum of space.

The new approach, which works at room temperature, opens up a world of possibilities for the use of magnetic fields to modulate light, with applications in autonomous vehicle sensors, communication in space, and optical wireless networks.

Minjeong holds a gel made up of chiromagnetic nanoparticles that are a conduit for modulating light. (Credit: Joseph Xu/U. Michigan Engineering)

To date, expensive rare-earth metals such as europium, cerium, and yttrium have been used to demonstrate how the path, speed, and intensity of optical, or light-based, signals can be controlled with magnetic fields. This capability is already in commercial use in high-speed fiber optic internet cables. But the elements’ cost and temperature needs have kept the technology from greater use.

A cost-effective, room temperature solution to magnetic control of twisted light could enable mass-market 3D displays, holographic projectors, and new generation of Light Detection and Ranging (LIDAR). LIDAR is one of the main technologies that give “sight” to autonomous vehicles.

“Many companies and labs developed exciting prototypes using magneto-optic technology,” says project leader Nicholas Kotov, professor of chemical engineering at the University of Michigan. “But their technological acceptance has been limited to date because of the fundamental materials issues with rare earth magneto-optics. It has been like trying to solve the Rubik’s Cube puzzle. You get one property right but lose the others.”

Minjeong Cha applies a gel made up of chiromagnetic nanoparticles that are a conduit for modulating light to a laser apparatus. (Credit: Joseph Xu/U. Michigan Engineering)

In a study published in Science, the researchers demonstrate that they could use nanoparticles based on inexpensive cobalt oxide—a white, magnetic semiconductor—to control twisted light well using magnetic fields.

The trick, the researchers found, was to twist the nanoparticles themselves by coating them with amino acids. The twist could be either right- or left-handed—a property called chirality.

The chirality of the nanoparticles produced a heightened sensitivity to magnetism and also strengthened interactions with twisted light—more formally referred to as “circularly polarized light.” The researchers demonstrated that by suspending the nanoparticles in a transparent, elastic, room-temperature gel, they could change the intensity of circularly polarized light by applying a magnetic field.

“This opens the road to the wide proliferation of magneto-optical devices with exciting possibilities emerging in 3D displays and real-time holography—all utilizing circularly-polarized light,” says Kotov, who is also a professor of materials science and engineering. “Furthermore, the small size of the nanoparticles enables their use in computer engineering and large-scale manufacturing of magneto-optical composites.”

Funding for the research came from the National Science Foundation and the Air Force Office of Scientific Research in the US, and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Conselho Nacional de Desenvolvimento Científico e Tecnológico, and Fundação de Amparo à Pesquisa do Estado de São Paulo in Brazil.

The University of Michigan is pursuing patent protection for the intellectual property and is seeking commercialization partners to help bring the technology to market.